Storage materials for hydrogen and other small molecules

ABSTRACT

This invention relates to adsorbents useful for storing hydrogen and other small molecules, and to methods for preparing such adsorbents. The adsorbents are produced by heating carbonaceous materials to a temperature of at least 900° C. in an atmosphere of hydrogen.

FIELD OF THE INVENTION

This invention relates to adsorbents useful for storing hydrogen andother small molecules, and to methods for preparing such adsorbents.

BACKGROUND OF THE INVENTION

The need for a clean energy source has stimulated much effort in pursuitof hydrogen-based fuel-cell technologies. Obstacles to solving thisproblem have been the lack of practical systems for hydrogen storage andan inability to identify the key factors that promote optimal hydrogenstorage. Adsorbents derived from carbonaceous materials have been widelystudied, but do not yet meet all the requirements for hydrogen storagecapacity, cost, and ease of manufacturing.

It has proved difficult to prepare carbon samples with high surfaceareas (1,500-3,000 m²/g) from a wide variety of carbonaceous precursors.Previous approaches typically involved pyrolysis in either an oxidizingatmosphere (e.g., air) or an inert atmosphere (e.g., nitrogen).Previously disclosed hydrogen treatment processes were conducted atlower temperatures (50-400° C.), and were designed to remove impuritieson the surface of fullerenes, carbon nanofibers, carbon nanotubes,carbon soot, nanocapsules, bucky onions, carbon fibers and othercarbonaceous material

Shiraishi et al. (US2003/0118907) disclose a hydrogen-storingcarbonaceous material obtainable by heating a carbonaceous material in agas atmosphere including hydrogen gas and substantially including noreactive gas as impurity gas.

Wojtowicz et al. (US2002/0020292) disclose a method for storing gas bycarbonizing a carbonaceous precursor material in a substantiallynonoxidizing atmosphere and at temperatures that attain an upper valueof at least 1000° C. (to produce substantial graphitization of thecarbon of the precursor material) and then introducing a gas (e.g.,hydrogen) to be stored, under positive pressure, into a storage vesselcontaining a substantial amount of the sorbent material.

Wojtowicz et al. (Int. J. Soc. Mat. Eng. Resources, Vol. 7, No. 2,253-266 (1999)) disclose the char-activation of polyvinylidene chlorideto form a hydrogen storage material with high micropore volumes. No datais provided on the structural characterization (i.e., crystallinity orpresence of turbostratic regions) of these materials.

Rodriquez et al. (U.S. Pat. No. 5,653,951) disclose a solid layerednanostructure comprised of crystalline regions, interstices (0.335 nm to0.67 nm) within the crystalline regions, and nanostructure surfacesdefining the interstices which have hydrogen chemisorption properties. Acomposition comprising the solid layered nanostructure with hydrogenstored in the interstices is also disclosed.

Nijkamp et al. (Appl. Phys. A 72, 619-623(2001)) and Chahine et al.(Hydrogen Energy Progress XI, Proceedings of the World Hydrogen EnergyConference, 11^(th), Stuttgart, Jun. 23-28, 1996, Vol. 2, 1259-1263)tabulate the hydrogen adsorption capacity, pore volumes and surfaceareas of several carbonaceous materials. No data is provided on thestructural characterization (i.e., crystallinity or presence ofturbostratic regions) of these materials.

Quinn et al. (U.S. Pat. No. 5,071,820) disclose a process for activatingcarbon to produce a carbon having a high micropore and low macroporevolume by a series of steps of heating the carbon in the presence ofoxygen, followed by heating the carbon in a nitrogen atmosphere. No datais provided on the structural characterization (i.e., crystallinity orpresence of turbostratic regions) of these materials.

In the last several years, much effort has been made to understand thecharacteristics of carbon adsorbents that correlate with high storagecapacity. Materials with high hydrogen storage capacity are of specialinterest. Nijkamp and others have observed that surface area seems to bea key factor for hydrogen storage, but it is clearly not the only one,since there is a great deal of scatter in the data for samples withmoderate surface areas (1,000-1,500 m²/g). Based on data obtained forthese moderate surface area carbons, it has also been proposed thatmicropore volume is another key factor, even though the hydrogenadsorption data is also badly scattered for this variable.

SUMMARY OF THE INVENTION

This invention provides a process for producing carbon nanostructures,comprising heating a carbonaceous material in the presence of H₂ to atemperature of at least 900° C.

This invention also provides carbon nanostructures made by heating acarbonaceous material in the presence of H₂ to a temperature of at least900° C.

This invention also provides carbon nanostructures characterized byhaving:

a. amorphous regions;

b. turbostratic regions;

c. surface areas of at least 1,500 m²/g; and

d. total pore volume of at least 0.5 cc/g.

This invention also provides a process for storing small moleculesselected from the group consisting of hydrogen, methane, oxygen,nitrogen and carbon dioxide, the process comprising introducing thesmall molecule into a storage vessel containing the carbonnanostructures of this invention.

This invention also provides a composition comprising carbonnanostructures characterized by having:

-   -   a. amorphous regions;    -   b. turbostratic regions;    -   c. surface areas of at least 1,500 m²/g; and    -   d. total pore volume of at least 0.5 cc/g.

The invention also provides a composition that comprises turbostraticregions that comprise greater than 50% of the composition.

The invention also provides a composition that comprises carbonnanostructures characterized by having total BET surface area of1500-2300 m²/g.

The invention also provides a composition that comprises carbonnanostructures characterized by having a total pore volume of 0.5-5.5cc/g.

The composition may further comprise adsorbed small molecules. Theadsorbed small molecules may be selected from the group consisting ofhydrogen, oxygen, nitrogen, methane and carbon dioxide. In someembodiments of the invention the adsorbed small molecule is hydrogen.The invention also includes a composition with adsorbed hydrogen whereinthe adsorbed H₂ comprises at least 1 wt % of the composition at 10 barand −160° C. to −180° C.

This invention also provides a process for separating mixtures of gases,comprising:

-   -   a. introducing a mixture of gases into a storage vessel        containing the carbon nanostructures of this invention;    -   b. allowing the gases to at least partially equilibrate at        elevated pressure to form adsorbed and non-adsorbed gases; and    -   c. reducing the pressure and removing at least a portion of the        non-adsorbed gases.

The process for separating mixtures of gases may further comprise thestep: d. further reducing the pressure and/or heating the carbonnanostructures to remove any additional non-adsorbed gases and at leasta portion of the adsorbed gases.

FIGURES

FIG. 1 a is a low magnification TEM (transmission electron micrograph)of the chitosan-derived adsorbent of Example 6, showing the presence ofboth turbostratic graphite ribbons (TER) and amorphous regions (AR).

FIG. 1 b is a high resolution TEM of a turbostratic region of theadsorbent of Example 6.

FIG. 1 c is a TEM of amorphous carbon which has no long range order.

FIG. 2( a) is a low resolution TEM of the chitin-derived adsorbent ofExample 7, showing the presence of turbostratic regions and amorphousregions.

FIG. 2( b) is a high resolution TEM of the chitin-derived adsorbent ofExample 7. The turbostratic graphitic sheets (TGS) are approximately50-60 nm long.

FIG. 3( a) is a low resolution TEM of the cellulose-derived adsorbent ofExample 14, showing the “ribbon-like” turbostratic regions and amorphousregions. The “ribbons” are up to 50 nm long.

FIG. 3( b) is a high resolution TEM of the cellulose-derived adsorbentof Example 14, showing clearly the graphite-sheet structure of the“ribbon-like” turbostratic regions.

FIG. 4 is a low resolution TEM of a sample of a commercial carbon (ChibaHSAG) showing the predominance of amorphous regions (AR) and the lack ofturbostratic features larger than about 3 nm.

FIG. 5 is a graph of wt % H₂ adsorbed (at T=−162° C.) vs. pressure for achitosan-derived (TM 1232) adsorbent sample treated at 1100° C. for 30hr with H₂.

FIG. 6 is a graph showing the pressure dependence (at T=−166° C.) of acellulose-derived hydrogen adsorbent treated at 1100° C. for 30 hr withH₂.

FIG. 7 is a graph showing DSC results for a chitosan-derived adsorbent.

FIG. 8 shows the DSC results as wt % H₂ adsorbed as a function ofpressure at room temperature for the untreated Darco carbon adsorbent ofExample 16, for comparison.

DETAILED DESCRIPTION OF THE INVENTION

Applicants provide a process to produce carbon nanostructurescharacterized by high surface area, high total pore volume, and highhydrogen storage capacity by the pyrolysis of carbonaceous materials athigh temperature (>900° C.) in the presence of hydrogen. These materialshave both amorphous (i.e., non-crystalline) and turbostratic regions.The hydrogen treatment process of this invention comprises heating thecarbonaceous material to a temperature of at least 900° C. in anatmosphere of hydrogen.

Carbonaceous materials suitable for use in this process includepolysaccharides, carbohydrates, natural and synthetic polymers, andactivated carbons. In one embodiment the carbonaceous materials areselected from chitosan, chitin, and cellulose.

In the process of this invention, the carbonaceous materials are heatedto a temperature of at least 900° C., and generally less than 1600° C.,for a time sufficient to generate the desired increase in pore volumeand/or surface area. Heating the materials at temperatures of 900-1200°C. requires longer heating times to generate a given pore volume orsurface area than heating an equivalent sample to 1200-1600° C. Heatingto temperatures greater than 1400° C., although operable, may bedetrimental to the storage capacity for hydrogen and other smallmolecules unless the heating time is kept very short (less than 1 hr).For many samples, heating to 1000-1200° C. for 2-48 hr provides thedesired substantial increases in surface area, total pore volume andstorage capacity. Optimizing the process conditions for a given type ofcarbonaceous precursor can done by optimizing one variable at a time(e.g., temperature, time, flow rate, etc.) or by a statistical design ofexperiments to optimize multiple variables simultaneously.

As is evident from the data in the Tables below, total BET surface areatends to increase with increasing pyrolysis temperature and/or holdtime, up to a maximum of almost 2300 m²/g for some samples. Pore volumesalso increase, up to about 5.3 cc/g. Further heating in hydrogen canresult in a dramatic decrease in surface area, total pore volume, andadsorption capacity.

Applicants have discovered that high hydrogen storage capacity can beachieved in carbons with essentially no micropore volume, and thatstorage capacity is better correlated with total pore volume than withmicropore volume. In the early stage of the pyrolysis, changes inmicropore volume tend to be small. Once the surface area reaches about1500 m²/g, the micropore volume has decreased to a negligible value, asmeasured by nitrogen porosimetry. Surprisingly, pyrolysis under hydrogendramatically increases the total pore volume for many samples, withmaximum total pore volume and maximum surface area being obtained atabout the same conditions of time and temperature for a given sample.

Transmission electron microscopy (TEM) reveals that the samples producedby this invention contain both amorphous regions and turbostraticregions. “Turbostratic” carbon is the term given to carbon morphology of2-dimensionally ordered carbon (essentially graphitic sheets of carbon)that is not ordered in the direction perpendicular to the plane of thesheets. Turbostratic carbon can be considered to be an intermediatestate in the transformation of amorphous carbon to graphitic carbon. Inthe carbon-based adsorbents used in this invention, the turbostraticregions contain turbostratic graphite fragments of at least 10 nm inlength. Another embodiment of the invention uses carbon-basedturbostratic graphitic fragments at least 20 nm in length.

Applicants speculate that the dramatic loss of surface area and porevolume observed for some samples may correspond to the transformationand consolidation of substantial portions of the carbonaceous materialinto these turbostratic, graphitic structures.

For use as hydrogen storage materials, carbons with both amorphous andturbostratic regions also preferably have total pore volumes of at least0.5 cc/g.

The carbon nanostructures made by the process of this invention may alsobe used to store other small molecules, such as methane, oxygen,nitrogen and carbon dioxide.

The process of storing small molecules in the carbon nanostructures ofthis invention is carried out by exposing the carbon nanostructures ofthis invention to the small molecule under a suitable combination ofpressure and temperature. Generally, low temperatures and/or highpressures are preferred to achieve high storage efficiencies (i.e., highwt % adsorbed small molecule).

The carbon nanostructures of this invention can also be used as theselective adsorbent in any one of several of the well-known gasseparation processes. An example of such a gas separation process is anadiabatic process known as PSA. It is used to purify gases by removingany accompanying impurities by adsorption through suitable adsorbents infixed beds contained in pressure vessels under high pressure. In a batchversion of a PSA process, a mixture of gases to be separated isintroduced into a pressure vessel that contains an adsorbent that has atleast some selectivity for a subset of the gases in the mixture. Afterthe gases have been introduced into the pressure vessel and been allowedto at least partially equilibrate, the pressure is reduced and at leasta portion of the non-adsorbed gases is removed. This portion of thegases will be selectively enriched in one or more of the gases in themixture and can be subjected to additional cycles of exposure toadsorbents at elevated pressure and removal at lower pressure.Similarly, the gases initially adsorbed onto the adsorbent can beremoved by further reducing the pressure and/or heating the adsorbent.These gases can also be subjected to additional cycles ofadsorption/desorption to further enhance the separation. PSA processesare frequently conducted in semi-batch mode using multiple pressurevessels (or adsorbent-loaded columns).

The carbon nanostructures of this invention can also be used in membraneseparation processes in which either the adsorbents are fabricated intothin-films for gas separation or are incorporated into polymer membranesfor increasing gas selectivity for a variety of gas separations. Suchapplications include but are not limited to separating oxygen andnitrogen from air, separating carbon dioxide and oxygen from air,separating hydrogen from syngas, separating hydrogen from hydrocarbons,and separating methane from natural gas.

Additional applications include using these materials in adsorptionrefrigeration cycles, purifying liquids such as water, and separatingcomponents from liquids. An example of the latter application isremoving proteins from fermentation broths.

EXAMPLES Electron Microscopy Procedures

Transmission electron microscopy (TEM) with atomic resolution andenvironmental transmission electron microscopy (ETEM) were used tounderstand the microstructure, morphology and chemical composition ofthe samples. Structural and high precision chemical compositionalanalyses were carried out using an advanced Tecnai field emission gunTEM/STEM instrument (Gai and Boyes, “EM in Het catalysi”, Inst ofPhysics Publ(UK and USA), 2003). Additionally, microstructuralinvestigations on the atomic scale at different temperatures wereperformed using a novel ETEM (Gai (E. I. du Pont de Nemours and Company,Wilmington, Del. USA), Advanced Materials, Vol 10, p. 1259, 1998)) usinga modified Philips* CM30 instrument. All the EMs were equipped withX-ray spectrometers to analyze chemical compositions. The chemicalcomposition analyses were performed by electron stimulated energydispersive X-ray compositional spectroscopy (EDX), providing highspatial resolution on the (sub) nanometer scale.

Examples 1-16 Materials

Food grade chitosan (ChitoClear®, Lot Nos. 66 and 1232) was purchasedfrom Primex Ingredients ASA (Avaldsnes, Norway). Chitosan 66 refers to amaterial with a molecular weight of about 385,000 g/mol. Chitosan 1232refers to a material with a molecular weight of about 171,000 g/mol.Chitin was also obtained from Primex Ingredients ASA. Cellulose wasobtained from Baker (Phillipsburg, N.J.). Darco carbon adsorbent wasobtained from Sigma-Aldrich (St. Louis, Mo.). Chiba HSAG was obtainedfrom Chiba University (Chiba, Japan).

Methods:

The carbon nanostructures used as hydrogen storage materials in theseexamples were prepared by placing weighed samples of carbonaceousprecursors into alumina and graphite boats that were then inserted intothe center of a tube furnace. The tube furnace was purged with ultrapure(99.995%) hydrogen at about 800 sccm. The furnaces were heated atapproximately 1° C./min to the specified hold temperature for thespecified hold time, and then allowed to cool under hydrogen to roomtemperature. The boats were removed and weighed to calculate yields. Inthe comparative examples described below, some of the carbonaceousprecursors were also treated under a flow of argon at about 800 sccm.

The storage materials were characterized using nitrogen porosimetry tomeasure surface area and pore volumes. The total surface area, themacroporous surface area (i.e., surface area for pores greater thanapproximately 20 A), and the microporous surface area (i.e., surfacearea with pores less than approximately 20 A), were measured usingstandard methods. The total pore volume and the macroporous pore volumewere also measured using standard methods; the microvolume volume iscalculated from the difference in total and macroporous volume. In theTables below, only the total surface area (BET SA), total pore volume(PV), and micropore volume (MPV) are reported.

The hydrogen storage capacities were measured using an intelligentgravimetric analyzer (IGA) from Hiden Isochema, Ltd., Warrington,England. Temperature was measured with a thermocouple placed slightlyabove the sample. A sample of about 50 to 100 mg was tested. Beforeexposing the sample to hydrogen, an outgas sequence was performed toremove any residual water or other contaminants in the sample. Thesample chamber pressure was reduced to 10⁻⁵ to 10⁻⁶ torr and the samplewas heated at 5° C./min to 250° C. for 6 hours or until no furtherweight loss was measured. The sample was allowed to cool down to roomtemperature and the pressure inside the chamber was increased withhydrogen to begin the hydrogenation sequence. In the hydrogenationprocess ultra-purified hydrogen (99.995%) was introduced into the samplechamber.

The pressure was increased to 10 mbar and the temperature was decreasedusing liquid nitrogen in a dewar surrounding the sample chamber. Whenthe temperature stabilized between −180 to −160° C., the pressure wasincreased in steps from 10 mbar up to a maximum of 10000 mbar (10.0bar). Applicants allowed the weight measurement at each step to reachequilibrium before proceeding to the next step. Once the final weightmeasurement was completed, the sample pressure was decreased in steps tomeasure hysteresis. The pressure, weight, and temperature of the samplewere continuously recorded.

The gravimetric microbalance results were corrected for buoyancy of thehydrogen gas as a function of both pressure and temperature.

The results for samples treated with hydrogen at 900-1000° C. for 2-48hours are summarized in Table 1 (containing Examples 1-16). H₂adsorption results (H2 ADS) were obtained at temperatures of −160° C. to−180° C., and at a pressure of 3,000 mbar. H2 ADS data in parenthesesindicate wt % H₂ adsorbed at 10,000 mbar.

Transmission electron micrographs of Examples 6, 7 and 14 are shownFIGS. 1 a-c, 2 a-c, and 3 a-c, respectively. The turbostratic regionsand amorphous regions can clearly be seen in these TEMs. FIG. 4 is a TEMof comparative sample of amorphous carbon (Chiba HSAG), in which theturbostratic regions contain fragment smaller than about 3 nm.

TABLE 1 Hydrogen Adsorption Properties Temp. Time Yield BET SA PV MPV H2ADS Ex. Material (° C.) (hr) (wt %) m²/g cc/g cc/g wt % 1 Chitosan 661100 30 2.5 1879 1.92 —  3.7 2 Chitosan 1232 1100 24 5.6 1828 1.45 — 2.3 3 Chitosan 1232 1100 24 3.4 2062 1.81 —  7.3 4 Chitosan 1232 110024 2.5 2153 2.01 —  8.4 5 Chitosan 1232 1100 30 2.4 1873 1.79 — 10.2 6Chitosan 1232 1100 36 1.3 1960 5.33 —  4.9 7 Chitin 1100 24 2.4 14052.37 — 10.5 8 Cellulose 900 2 8.9 524 0.25 0.20  1.1 (2.6) 9 Cellulose1000 2 7.9 814 0.38 0.30  1.6 (3.0) 10 Cellulose 1100 2 4.4 1505 0.770.46  2.0 (4.2) 11 Cellulose 1200 2 2.8 1803 1.43 —  2.5 (5.7) 12Cellulose 1100 12 1.6 2127 2.04 —  2.8 (6.0) 13 Cellulose 1100 24 1.91842 2.09 —  2.3 (5.3) 14 Cellulose 1100 36 — 1560 2.04 —  4.2 (10.4) 15Cellulose 1100 48 1.8 1355 1.90 —  2.2 (5.2) 16 Darco 1100 24 — 2292 3.8—  3.1 (5.2) BET SA = BET surface area PV = total pore volume MPV =micropore volume H₂ ADS = wt % H₂ adsorbed at 3,000 mbar by H₂-treatedcarbon material; data in parentheses is wt % H₂ adsorbed at 10,000 mbar.

Examples 17-23 and Comparative Examples A-C

Samples of chitosan (ChitoClear®, Lot No. 656, molecular weight=about66,000 g/mol, Primex Ingredients ASA) were treated as described abovefor Examples 1-16, except that for the comparative examples A-C., argonwas used instead of hydrogen. The results are summarized in Table 2.

A second chitosan sample, (ChitoClear®, Lot No. 1111, molecularweight=about 342,000 g/mol; Primex Ingredients ASA), was heated asdescribed above for Examples 1-16, except that argon was used instead ofhydrogen. This treatment produced results (not shown) that were similarto those of Examples 17-23 in which heating in an argon atmosphere attemperatures from 600-1200° C. was shown to be ineffective in increasingsurface area of the sample. Heating chitosan (ChitoClear®, Lot No. 1111)to 900-1150° C. for 2-30 hours in hydrogen increased the BET surfacearea to as much as 1635 m²/g.

TABLE 2 Chitosan 656 Samples Treated in Hydrogen or Argon Temp. TimeYield BET SA PV Ex. Gas (° C.) (hr) (%) m²/g cc/g 17 H2 900 2 20.7 4440.1942 18 H2 1000 2 19.2 594 0.2612 19 H2 1100 2 17.8 412 0.1830 20 H21100 6 9.5 1534 0.7655 21 H2 1100 12 4.3 2120 1.5479 22 H2 1100 24 2.01006 1.3303 23 H2 1100 48 0.6 116 0.2305 A Ar 800 2 30.4 <1 — B Ar 10002 27.4 <1 — C Ar 1200 2 27.1 <1 — BET SA = BET surface area PV = totalpore volume MPV = micropore volume H₂ ADS = wt % H₂ adsorbed at 3,000mbar by H₂-treated carbon material; data in parentheses is wt % H₂adsorbed at 10,000 mbar.

These results demonstrate that heating carbonaceous materials at hightemperatures in the presence of an inert gas does not necessarily leadto the formation of high surface area adsorbents.

Example 24 Pressure dependence of Hydrogen Adsorption

A sample of chitosan (ChitoClear®, Lot No. 1232) was treated withhydrogen at 1100° C. for 30 hr, as described above for Example 5, andthen exposed to hydrogen at pressures from 10 mbar to 3,000 mbar. FIG. 5shows the wt % H₂ adsorbed at T=−162° C. as a function of pressure.

FIG. 6 shows the wt % H₂ adsorbed at T=−166° C. as a function ofpressure for the cellulose-derived hydrogen adsorbent of Example 14. Theadsorbent was treated with hydrogen at 1100° C. for 36 hours.

Example 25 DSC of Chitosan-Derived Hydrogen Adsorbent Exposed toHydrogen

Approximately 2 mg of a sample of chitosan (ChitoClear®, Lot No. 1232)previously treated at 1100° C. for 24 hr with H₂, was lightly packedinto an open aluminum sample pan and installed in a differentialscanning calorimeter (TA Instruments, model Q10, New Castle, Del.) witha blank aluminum reference pan. The instrument was run according to themanufacturer's instructions for sub-ambient temperatures and hydrogenunder ambient pressure. A dewar was installed over the pans and filledwith liquid nitrogen until the sample temperature was approximately−173° C. The dewar was quickly removed, the sample cell was quicklyclosed with the steel cover, the sample gas overhead was quickly flushedwith helium, and finally the sample gas overhead was filled withhydrogen gas at approximately 1 atm pressure. The sample temperature wasallowed to warm to room temperature at a rate of approximately 10°C./min while the Q10 instrument recorded the heat flow differentialbetween the sample and reference pans. This signal was then reduced by acontrol signal obtained from the instrument under identical conditions,except that the sample pan was empty. The net signal provides the heatflow due only to the sample, as shown in FIG. 7.

An endothermic heat of approximately 9.1×10⁴ J/kmol is measured attemperatures below approximately 20° C., consistent with thevaporization of condensed hydrogen phase within the sample.

Example 26 High Pressure Dependence of Hydrogen Adsorption

A sample of Darco carbon was treated with hydrogen at 1100° C. for 24hr, as described above for Example 16, and then exposed to hydrogen atpressures from 1 bar to 1360 bar (14.7 to 20,000 psia). FIG. 8 shows thewt % H₂ adsorbed as a function of pressure at room temperature.

For comparison, FIG. 8 shows the wt % H₂ adsorbed as a function ofpressure at room temperature for the untreated Darco carbon adsorbent ofExample 16.

1. A process for producing a composition that comprises carbonnanostructure, comprising heating a carbonaceous material in thepresence of H₂ to a temperature of at least 900° C. for a timesufficient to generate an increase in pore volume and/or surface area ofthe material and form the carbon nanostructure, wherein the carbonaceousmaterial is selected from the group consisting of polysaccharides,carbohydrates, and natural polymers.
 2. The process of claim 1 whereinthe weight percent yield of solid carbonaceous material after saidheating is at least 0.6%.
 3. The process of claim 1, wherein thecarbonaceous material is heated to a temperature of 900-1600° C.
 4. Theprocess of claim 3, wherein the carbonaceous material is heated to atemperature of 1000-1200° C. for 2-48 hr.
 5. The process of claim 1,wherein the heating is in the presence of a substantially H₂ atmosphere.6. The process of claim 5, wherein the heating is for 2-48 hours.
 7. Theprocess of claim 1, wherein the carbon nanostructure comprises a.amorphous regions; b. turbostratic regions; c. a total BET surface areaof at least 1,500 m²/g; and d. total pore volume of at least 0.5 cc/g.8. The process of claim 7, wherein the turbostratic regions comprisegreater than 5000 of the nanonstructure.
 9. The process of claim 7,wherein the total BET surface area is 1500-2300 m²/g.
 10. The process ofclaim 7, wherein the total pore volume is 0.5-5.5 cc/g.
 11. The processof claim 1, wherein the carbonaceous material is a natural polymer. 12.The process of claim 11, wherein the natural polymer is selected fromthe group consisting of chitosan, chitin, and cellulose.
 13. The processof claim 12, wherein the natural polymer is heated to a temperature of1000-1200° C. for 2-48 hr.
 14. The process of claim 13, wherein theheating is in the presence of a substantially H₂ atmosphere.
 15. Aprocess for producing a composition that comprises carbon nanostructure,comprising heating a carbonaceous material in the presence of H₂ to atemperature of 1000° C. to 1600° C. for a time sufficient to generate anincrease in pore volume and/or surface area of the material and form thecarbon nanostructure, wherein the carbonaceous material is a syntheticpolymer.
 16. The process of claim 15, wherein the carbonaceous materialis heated to a temperature of 1000-1200° C. for 2-48 hr.
 17. The processof claim 16, wherein the heating is in the presence of a substantiallyH₂ atmosphere.